1. Field of the Invention
The invention pertains to the field of dry metalized film AC motor run capacitors and in particular to dry metalized polypropylene capacitors having a pressure sensitive fault interrupter.
2. Description of the Prior Art
There is virtually no known prior art either in printed literature or commercially available in the area of dry metalized film capacitors having fault interrupters.
British Pat. No. 1,569,186 discloses a film capacitor in which the capacitor roll deforms when heated, breaking a contact. It is unclear whether a dry or wet capacitor is intended. The problem with this device is that by the time the internal temperature is high enough to deform the film roll, some other interruption would have occurred, such as an explosion.
U.S. Pat. No. 3,496,432 also pertains to a dry capacitor relying on temperature to break a contact.
U.S. Pat. No. 3,909,683 teaches a pressure-sensitive fault interrupter in a dry film capacitor. It provides a yielding cavity with a fusible portion of one lead wire passing therethrough. In the event of over-pressure caused by a fault, at least one contact bridge is separated. Unfortunately, gases accumulate in the cavity and can be ignited by the breaking contact. The device tends to be too explosive for commercial use.
No dry film capacitors with fault interrupters are commercially available, indicating that the few devices disclosed in the patent literature have no commercial value, despite a proposed UL requirement in Capacitor-UL-810.
The literature on wet film capacitors with fault interrupters is extensive. Typical recent U.S. patents are Nos. 4,398,782 and 4,454,561.